1. Field of the Invention
The invention relates to sliding contact assemblies, in particular slip-rings and also slip-conductors as used for contacting transmission of electric signals or energy between movable parts.
2. Description of the Prior Art
For satisfactory performance of slip-rings and also slip-conductors, hereunder summarily designated by the generic term “sliding-contact assemblies,” it is absolutely essential to ensure or maintain an electrical insulation during operation. Sliding-contact assemblies frequently have the problem of contamination which is detrimental to the insulation. Sliding-contact assemblies are frequently of a size that does not permit their being completely encapsulated. Thus, it is hardly possible to completely enclose a slip-conductor having a length of many meters. Similarly, this is possible only with large outlay in the case of slip-rings that frequently are manufactured to have diameters of more than one meter. An ingress of dust and dirt into the sliding-contact assembly must therefore be expected. A far greater problem is usually posed by contamination generated within the sliding-contact assembly itself. Contact brushes are frequently made of conductive material compositions using graphite and metals such as silver, for example. When these contact brushes slide along the slide-tracks during operation, they are continually slightly abraded. The abraded matter passes into the surroundings in the form of a fine dust. This dust possesses a relatively high conductivity, as do the contact brushes, and frequently leads to an impairment of the insulation after a short period of operation.
Thus, when sliding-contact assemblies are designed, the insulating spaces between the slide-tracks and between the contact brushes, as prescribed by the applicable safety regulations, must be maintained. In fact, however, substantially larger insulating spaces, in particular creep paths, are provided in order to maintain the insulation even at given levels of contamination. The demands made on the creep paths then lead to designs requiring high outlay, as disclosed for example in U.S. Pat. No. 5,745,976. Disadvantages of large spaces or barriers of this kind between the slide tracks are the large requirements of space and the high manufacturing cost. At the same time, periods between maintenance operations during which the insulation must be cleaned are usually necessarily short . Cleaning methods of this kind involve relatively large outlay and are time-consuming because the abraded matter usually adheres to the surface very strongly.
In order at least to render difficult an entry of dust through gaps in a closed casing, DE 100 11 999 A suggests providing a dust trap or dust barrier. The surface of this is provided with a specially configured microstructure on which dust adheres particularly well. With this, a migration of the dust into the casing can be prevented effectively. A dust barrier of this kind is unsuitable for use in slip-rings or slip-conductors, because the dust is already being created by brush abrasion inside the assembly itself, and does not first have to migrate into this from the outside. A surface of this kind, on which dust is preferably deposited, would even lead to a more rapid accumulation of matter abraded from the brush, and therewith to an even more rapid deterioration of the insulation.
In DE 10118351 so-called self-cleaning surfaces are disclosed in which the self-cleaning effect, similar to that of the know lotus-effect, is based on water drops running off from the surface and carrying away the dirt lying on the surface. Self-cleaning of this kind only operates on surfaces that regularly come into contact with water. This is the case, for example, with surfaces that are exposed to the weather, and therefore regularly come into contact with rain water. Similarly, self-cleaning would be possible with surfaces that can be washed clean with water. In order for the described self-cleaning effect to operate, it is insufficient for the surfaces to be wiped with a damp cloth. Rather than this, drops must be able to form on the surface. Mechanical cleaning, for example with a damp cloth, may lead to damaging the surface, and also to the dirt particles being pressed into the surface, so that it can no longer be cleaned by the self-cleaning effect. Especially with electrical or electronic instruments and systems in which sliding-contact devices are used, a cleaning under running water is out of the question from the start. Even only damp cleaning, which in any case would not lead to the self-cleaning effect, cannot be performed in many cases because of a sensitivity of the surfaces to corrosion.
In DE 10219958 an electrical sliding contact arrangement is disclosed in a general form. Screen surfaces of electrically conducting material are provided between the slide tracks.
DE 2539091 discloses a sliding contact arrangement in which the slide tracks are mounted on electrically insulating material.
In WO 03/072849 a self-cleaning substrate surface is disclosed which is configured as a double structure having an overlying fine structure of 1-250 nm.